I. Field of the Invention
The present invention concerns the manufacture and use of polycrystalline diamond drilling bits.
More specifically, it is a means to produce drilling bits using thermally stable diamonds (hereinafter called TSP cutters) that are more predictable and cost effective than state of the art TSP cutter drill bits.
II. Description of the Prior Art
A typical prior art TSP cutter diamond bit is manufactured by forming a cavity in a suitable refractory material mold cavity (i.e. graphite) that is the mirror image of the desired finished product. The TSP cutters are then temporarily affixed with an adhesive in circumferentially placed vee shaped grooves formed in the mold. The entire bit head is then fabricated with materials and by technology well known in the diamond bit industry.
One typical example of prior art, Pat. No. 4,491,188 teaches a method for TSP cutter placement in circumferential V-groove segments in the aforesaid mold cavity The TSP cutters are basically triangular prisms. The cutter is positioned in the mold with a triangular face forward in the direction of rotation of the finished bit. An apical edge of the triangular prism is placed concurrent with the circumferentially oriented v-groove. The depth of the v-groove is such that the TSP cutter protrudes on the finished bit somewhat more than need be for optimum cutter strength and drilling fluid control. This is because the 60.degree. apical angle of the TSP cutter is very fragile and a portion of the cutting tip of somewhat unpredictable dimension is quickly broken or worn off as the bit is rotated at the bottom of the borehole.
To ensure that too large a portion of the TSP cutter is not broken off in shear, matrix back-up metal is formed in front of the leading and behind the trailing faces of the TSP cutter.
The following Pat. Nos. 4,529,047; 4,673,044; 4,744,427; 4,586,574 and 4,515,226, all teach basically the same triangular prisms as cutting elements positioned in circumferential v-groove segments with matrix metal back-up. All bits made to the specifications of the aforesaid patents, as well as Patent No. 4,491,188, have the same unpredictable "breaking-in" time and results, which can have severe deleterious effects on the drilling fluid flow velocities across the cutting structure. This unpredictable cutter height breakage results in uneven cutter loading with subsequent selective wear which leads to termination of the bit run.
In summary, the foregoing patents provide evidence of intense efforts in the prior art to develop a TSP cutter bit that overcomes some of the inadequacies described. Specifically, there is need in the art for thermally stable diamond drag bits that do not require a break-in period and the drilling fluid is controlled to a degree that diamond wear is an insignificant problem.